[MW] Need help on Heroic Will of the Emperor

We just had a night of wipes on this boss, and I honestly don't know what Mistweavers are supposed to do to handle the tank damage. We are 2-healing it, and I cannot keep my Tank alive. It seemed like there would be stretches where the tank wouldn't dodge, and even with good Chi generation from Soothing, I would have to Surge 2-3 times to keep him alive, and I don't have the mana to continue doing that. Without good RNG on Soothing Mist, I would oom almost instantly, or just flat out lose my Tank. Is there something I'm not understanding about single target healing, or do we just need to use cooldowns better?

Healing Sphere is difficult to use, but much higher HPS and HPM than a Soothing/EM rotation (yes, this factors in Mana Tea). It also overheals for less and you can hold it until you need it rather than constantly spending mana on tanks that might not need it at the time.